Elevated carbon dioxide levels increase production, but change soybean quality

Increased carbon dioxide concentration can offset some of the losses caused by heat and drought in soybeans, but it alters the nutritional composition of the grains. A study combined controlled trials and predictive modeling to evaluate yield, carbohydrates, lipids, proteins, and amino acids in scenarios associated with climate change.

Researchers observed up to a 142% increase in grain production under elevated carbon dioxide conditions. Conversely, high temperatures reduced production by 91%, and drought reduced it by 60%. The so-called "Triple Effect" scenario, with elevated carbon dioxide, high temperatures, and drought, indicated a potential increase of 50% in grain production, as well as a 35% increase in soluble sugars and a 175% increase in amino acids. The same scenario projected a 20% decrease in starch and a 6% decrease in protein.

Study form

The study used soybean plants of the MG/BR-46 Conquista cultivar, from Embrapa. Cultivation took place in open chambers in São Paulo, between September 2018 and February 2019. The treatments compared ambient carbon dioxide, at 400 ppm, and elevated carbon dioxide, at 800 ppm. One experiment added a temperature 5°C above ambient. Another evaluated water deficit after flowering, with irrigation suspended and then a restricted supply of 100 mL of water every three days until physiological maturity.

The plants were harvested at 60 and 125 days after emergence. Researchers used dry biomass at 60 days as an initial indicator. Then, they compared this data with grain yield and composition at 125 days. The analyses involved soluble sugars, starch, amino acids, lipids, carbon, nitrogen, and protein.

High carbon dioxide

The response to elevated carbon dioxide maintained a positive pattern for grain production in both experiments. In combination with high temperature, elevated carbon dioxide attenuated heat stress. Treatment with elevated temperature alone led to 0,63 g of grain per plant. The combination of elevated carbon dioxide plus temperature reached 16,9 g per plant.

The drought also affected grain formation. The water deficit treatment reached 2,78 g per plant. The combination of high carbon dioxide and drought reached 4,04 g per plant. Scientists point out that this is still a significant reduction, but less than under drought conditions without high carbon dioxide.

Grain quality

The quality of the grains changed distinctly between the treatments. Elevated carbon dioxide favored carbon assimilation and carbohydrate storage. High temperature and drought induced metabolic adjustments, with alterations in sugars and amino acids. These changes have implications for the nutritional quality of the grains.

In the oil, high temperature increased the proportion of palmitic, stearic, and oleic acids. The increases reached 14%, 7%, and 28%, respectively. Treatments with high temperature and with high carbon dioxide plus high temperature reduced the polyunsaturated fatty acids linoleic and linolenic. Drought reduced the relative abundance of palmitic, linoleic, and linolenic acids, but increased oleic acid.

Amino acids responded strongly to stress. The combination of high carbon dioxide plus temperature showed the highest level, five times higher than the ambient treatment. Temperature alone led to a fourfold increase. Drought increased amino acids threefold. The combination of high carbon dioxide plus drought increased them twofold. Despite this, total nitrogen and crude protein did not vary significantly between experimental treatments.

Modeling in the study

Modeling played a central role in the study. Generalized linear models used total biomass at 60 days to predict production and quality at 125 days. The models showed good approximation between observed and predicted values. Production under elevated carbon dioxide, for example, had an observed value of 16,9 g and a predicted value of 16,56 g.

Path analysis indicated a significant relationship between biomass at 60 days and grain yield at 125 days. Elevated carbon dioxide and the combination of elevated carbon dioxide plus temperature had positive effects on yield. Temperature, drought, and elevated carbon dioxide plus drought had negative effects.

For the “Triple Effect,” the researchers used machine learning. XGBoost showed the lowest error in estimating production under the combined scenario. The model projected 10,46 g of grains, with an RMSE of 0,04. CatBoost projected 10,51 g, with an RMSE of 1,50. For the other quality attributes, XGBoost also outperformed CatBoost.

Scientists highlight an important limitation: the “Triple Effect” has not undergone direct experimental validation. The projection resulted from the integration of validated data from dual stresses, such as elevated carbon dioxide plus temperature and elevated carbon dioxide plus drought. The study also took place in open chambers and with a specific cultivar. Therefore, the researchers indicate a need for validation under field conditions.

The study was conducted by Janaina da Silva Fortirer, Adriana Grandis, Carmen Eusebia Palacios Jara, Débora Pagliuso, Leandro Francisco de Oliveira, Eveline Queiroz de Pinho Tavares, Lauana Pereira de Oliveira, Plínio B. Camargo, Eny Iochevet Segal Floh, Cibele M. Russo, and Marcos S. Buckeridge.

Further information can be found at doi.org/10.1016/j.foodres.2026.119004